The present invention relates to pallets and more particularly to pallets of moulded plastics construction, and to moulding apparatus for producing such pallets and other plastics articles.
The present applicants and their successors in business have devised a range of plastics pallets of one-piece moulded plastics construction formed by an injection moulding technique using either wholly or partially post-consumer recycled plastics. While these pallets are effective in use, the applicants have determined that it would be of advantage to construct a pallet of lighter weight whilst achieving similar strength characteristics to those of their earlier pallets.
More particularly there is disclosed in International Patent Application No. PCT/AU97/00382, the disclosure of which is hereby incorporated by reference, a load-carrying pallet moulded in one piece in a suitable plastics, for example post-consumer recycled plastics. International Patent Application PCT/AU95/00690 also discloses a load-carrying pallet formed as a one-piece plastics moulding. We are now proposing to produce a pallet of the type disclosed in the aforesaid applications but using less plastics material. This will be achieved by using thinner sections for the load carrying platform, the beams beneath the platform, and the ground-engaging struts at the underside of the pallet. However in order to achieve adequate rigidity of the overall structure we are proposing to reinforce the load-carrying platform by moulding a multiplicity of intersecting webs into the underside of the load carrying platform whereby the ribs intersect to define a cellular structure with the cells distributed throughout the exposed parts of the underside or at least in those parts subject to maximum loading. For example, the cellular structure may be of honeycomb form or alternatively the cells may be of rectangular or diamond shape. In each case, the axis of each individual cell will extend perpendicularly to the plane of the load carrying surface and each cell will be open at its underside.
According to one aspect of the present invention, there is provided a pallet of moulded construction comprising a load-carrying surface supported by underlying support structure configured to permit the insertion of the tines of the fork-lift, the load-carrying surface being reinforced at its underside by a cellular reinforcing structure comprising g cells the axes of which extend perpendicularly to the load-carrying surface.
Advantageously, the underlying support structure comprises a series of parallel beams of hollow construction comprising opposed side walls, the beams being internally reinforced by webs defining a cellular structure extending to the underside of the load-carrying platform, and the axes of the cells of the reinforcing structure within the beams being substantially perpendicular to the load-carrying platform.
Advantageously, the beams have transverse apertures to permit insertion of the tines of a fork-lift laterally to the beams, and the cellular reinforcement of the load-carrying platform in the zone of the platform adjacent the lateral apertures in the beams has a smaller cell size than that in other zones of the load-carrying platform.
Advantageously, the entire pallet is constructed in a single moulding operation and the mould incorporates a retractable core for forming the cellular reinforcement at the underside of the platform in the zones thereof adjacent the lateral apertures in the beams.
Advantageously, the cellular reinforcing structure in the beams extends to the underside of the beams, and the load-carrying platform is configured to define a pattern of upstanding projections and lands around the projections whereby when two like pallets are arranged in stacked relationship, the lower edges of the reinforcing cells of the beams of the upper pallet will engage with the lands on in the load-carrying platform of the lower pallet whereby to prevent slippage between the two pallets.
According to another aspect of the present invention there is provided an injection mould having a retractable mould core structure, said mould core structure comprising a retractable core configured to form cellular or other reinforcing structure at an inner surface of an article being moulded, and means for retracting said core in a direction substantially at right angles to said surface, said retracting means comprising at least one driving member mounted for reciprocatory movement in a direction at right angles to the direction of retraction, and means linking said driving member and core to translate said movement of the driving member into the required. movement of the core.
In a preferred embodiment of the invention the linkage provided between the core and the driving member is provided by one or more cooperating cams and cam tracks.
Advantageously, the driving member comprises a strip having a series of driving cams, said strip cooperating with a corresponding strip carried by the core and providing a series of cam tracks which cooperate with the respective cams such that movement of the driving strip in one direction causes retraction of the core and movement in the opposite direction causes extension of the core into an operative position for moulding. Preferably there are two or more such driving strips arranged in parallel relation and each cooperating with a respective strip carried by the core.
Preferably, the or each driving strip is driven by a fluid cylinder.
Advantageously, the cams and cam tracks cooperate when the core is in its operative moulding position to lock the core in that position against the pressure of the material being moulded.
The present invention also provides a method of injection moulding plastics articles using a retractable core structure as defined above.
The present invention also provides a moulded plastics article when produced by use of a mould incorporating a retractable core structure as defined above.